Enable font-synthesis-weight support for servo (#244)

* parse font-synthesis-weight for servo

Signed-off-by: minghuaw <[email protected]>

* derive Serialize and Deserialize for FontSynthesis

Signed-off-by: minghuaw <[email protected]>

* derive Hash for FontSynthesis

Signed-off-by: minghuaw <[email protected]>

* restore mistakenly removed Serialzie and Deserialze derive

Signed-off-by: minghuaw <[email protected]>

---------

Signed-off-by: minghuaw <[email protected]>

Author: minghuaw

style/properties/cascade.rs

@@ -1074,7 +1074,6 @@ impl<'b> Cascade<'b> {
             builder.add_flags(ComputedValueFlags::HAS_AUTHOR_SPECIFIED_WORD_SPACING);
         }
 
-        #[cfg(feature = "gecko")]
         if self
             .author_specified
             .contains(LonghandId::FontSynthesisWeight)

style/properties/longhands/font.mako.rs

@@ -87,7 +87,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "font-synthesis-weight",
     "FontSynthesis",
-    engines="gecko",
+    engines="gecko servo",
     initial_value="computed::FontSynthesis::Auto",
     initial_specified_value="specified::FontSynthesis::Auto",
     gecko_ffi_name="mFont.synthesisWeight",

style/values/specified/font.rs

@@ -1522,6 +1522,7 @@ impl Parse for FontLanguageOverride {
     Copy,
     Debug,
     Eq,
+    Hash,
     MallocSizeOf,
     Parse,
     PartialEq,
@@ -1531,6 +1532,7 @@ impl Parse for FontLanguageOverride {
     ToResolvedValue,
     ToShmem,
 )]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub enum FontSynthesis {
     /// This attribute may be synthesized if not supported by a face.
     Auto,